DE102019215618A1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine in which the internal combustion engine is operated from a first operating state (43) under predeterminable conditions during operation of a tank heater of a reducing agent tank and operated in a second operating state (44) for the duration of the limitation.

Description

The present invention relates to a method for operating an internal combustion engine. The present invention also relates to a computer program that executes each step of the method, as well as a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

In order to reduce the proportion of nitrogen oxides in the exhaust gas of an internal combustion engine, in particular a diesel engine, it is known to arrange an SCR (selective catalytic reduction) catalyst in an exhaust line. This reduces the nitrogen oxides contained in the exhaust gas in the presence of ammonia as a reducing agent to nitrogen. In order to provide the ammonia, a reducing agent solution is metered into the exhaust system upstream of the SCR catalytic converter. As a rule, an aqueous urea solution (urea water solution; HWL) containing urea as an ammonia-releasing reagent is used for this. A 32.5 percent HWL is commercially available ^{under the name AdBlue ®.} This has a freezing point of -11.5 ° C.

At ambient temperatures below the freezing point of AdBlue ^® , the HWL would freeze. To prevent this when the SCR catalytic converter system is in operation, a tank heater is provided in the reducing agent tank. However, if a motor vehicle in which the SCR catalytic converter system is arranged is parked for a long time at low outside temperatures, the HWL freezes because the tank heating is switched off when the vehicle is parked. By switching on the tank heater, the HWL must first be thawed when the vehicle is started up again so that it can be metered into the exhaust system. The tank heating and thermal insulation of the reducing agent tank are dimensioned in such a way that, in most cases, sufficient HWL can be thawed quickly to meet the HWL requirements of the SCR catalyst system, but there are exceptions. If a motor vehicle is parked for a long time at a low outside temperature in regions with very cold winters, the frozen HWL in the reducing agent tank takes on such a low temperature that it takes a long time to thaw. If the internal combustion engine is subjected to high loads during the thawing process because the motor vehicle is heavily loaded and the driver may be driving aggressively, it can happen that the entire thawed HWL is metered into the exhaust system due to metering requirements. This means that the tank heater is no longer surrounded by liquid HWL, but only by air. This means that it cannot transfer any more heat to the frozen HWL, which is isolated from the tank heater by an air bubble. This would lead to the SCR catalytic converter system no longer working.

In order to prevent this, operating strategies of the SCR catalytic converter system are used in which the maximum permissible dosing rate of the HWL is limited during a thawing phase of the HWL under critical conditions with regard to the ambient temperature and load requirements on the internal combustion engine. This limitation can prevent a complete failure of the SCR catalytic converter system, but it is no longer possible to completely reduce the nitrogen oxide emissions of the internal combustion engine, so that nitrogen oxides are released into the environment.

Disclosure of the invention

In the method for operating an internal combustion engine, the internal combustion engine is switched from a first operating state to a second operating state under predeterminable conditions during operation of a tank heater of a reducing agent tank of an SCR catalytic converter system of the internal combustion engine.

The prescribable conditions preferably include that the prescribable conditions include that the prescribable conditions include that the phase state of a reducing agent solution in the reducing agent tank was determined as frozen or partially frozen by a model. This indicates that it is necessary to thaw the reducing agent solution.

Furthermore, it is preferred that the specifiable conditions include that an ambient temperature of the reducing agent tank falls below a specifiable first temperature threshold value, at least for a specifiable first period of time. Under these conditions, it can be assumed that the frozen reducing agent solution in the reducing agent tank has assumed such a low temperature that it can only be thawed slowly by means of the tank heater.

Furthermore, it is preferred that the predefined conditions include that a temperature of the reducing agent tank falls below a predeterminable temperature threshold value at least for a predeterminable second period of time. Even under these conditions, it can be assumed that the frozen reducing agent solution in the reducing agent tank can only be thawed slowly by means of the tank heater.

In addition, it is preferred that the predeterminable conditions include that a signal from a concentration sensor of the reducing agent tank is not available. This indicates that the concentration sensor is trapped in frozen reductant solution.

Furthermore, it is preferred that the predeterminable conditions include that a signal from a fill level sensor of the reducing agent tank is not available. This indicates that the level sensor is trapped in frozen reductant solution.

Finally, it is preferred that the predeterminable conditions include that a modeled amount of liquid reducing agent solution falls below an amount threshold value. This model can be based on a mass balance of reducing agent solution metered into the exhaust system. The quantity threshold value can be selected so that if it falls below it, there is a risk of imminent consumption of the remaining liquid reducing agent solution.

The method provides that the internal combustion engine is operated in the first operating state without the prescribable conditions and is operated in the second operating state for the duration of the prescribable conditions. The first operating state corresponds to an operating state of a conventional operating strategy of the internal combustion engine. The second operating state can be designed in such a way that the raw emissions of the internal combustion engine of nitrogen oxides are reduced compared to the first operating state in order to reduce or even completely eliminate the negative effects of operating the SCR catalytic converter system with a limited metering rate on the environment.

This is preferably achieved in that the internal combustion engine is operated in the second operating state in such a way that raw nitrogen oxide emissions of the internal combustion engine are reduced compared to the first operating state. This operation of the internal combustion engine can be implemented by an electronic control unit. This can be the same electronic control unit that also operates the SCR catalytic converter system. However, it is also possible to operate the internal combustion engine via an engine control unit which only receives data from another control unit that controls the SCR catalytic converter system.

In a preferred embodiment of the method, the reduction in nitrogen oxide emissions is achieved in that a torque of the internal combustion engine is limited in the second operating state. This prevents high torque requirements from the driver of a motor vehicle driven by the internal combustion engine. In order to avoid high nitrogen oxide emissions, a lower speed of the motor vehicle is accepted.

In another preferred embodiment of the method, the internal combustion engine is operated in the second operating state with a different characteristic map than in the first operating state. This other characteristic map can be designed in such a way that the combustion processes in the internal combustion engine lead to lower raw nitrogen oxide emissions than in the first operating state. Such a change in the characteristic map is usually bought at the price of higher carbon dioxide emissions and higher fuel consumption of the internal combustion engine.

The characteristics map of the second operating state can in particular be designed in such a way that it provides a lower average combustion temperature of the internal combustion engine compared to the first operating state. This can be achieved, for example, by changing the fuel injection quantity or the air / fuel ratio. Alternatively or additionally, a higher exhaust gas recirculation rate (EGR rate) of the internal combustion engine compared to the first operating state is provided in the second operating state.

In addition to the anyway lower dosing of reducing agent solution into the exhaust system due to the reduced nitrogen oxide emissions of the internal combustion engine in the second operating mode, it can also be provided that a metering rate of at least one metering valve of the SCR catalytic converter system is limited in the second operating mode. This is a strategy known from the prior art for limiting the dosing rate in order to avoid failure of the SCR catalytic converter system. If the SCR catalytic converter system only has a single metering valve, the metering rate limitation is only applied to this. If it has several metering valves, the metering rate limitation is applied to all metering valves in such a way that a maximum total metering rate is not exceeded and therefore no more than a predetermined amount of reducing agent solution is withdrawn from the reducing agent tank within a predetermined period of time.

The computer program is set up to carry out each step of the method, in particular when it runs on a computing device or on an electronic control device. It enables the implementation of different embodiments of the method on an electronic control unit without structural changes to it to have to make. For this purpose, it is stored on the machine-readable storage medium.

By uploading the computer program to a conventional electronic control device, the electronic control device is obtained, which is set up to operate an internal combustion engine by means of the method.

Figure list

• 1 zeigt schematisch einen Verbrennungsmotor, der mittels eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens betrieben werden kann, zusammen mit seinem SCR-Katalysatorsystem.
• 2 zeigt ein Ablaufdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows schematically an internal combustion engine which can be operated by means of an exemplary embodiment of the method according to the invention, together with its SCR catalytic converter system.
• 2 shows a flow chart of an embodiment of the method according to the invention.

Embodiments of the invention

An internal combustion engine 10 , a motor vehicle not shown, is in 1 pictured. It emits raw emissions in an exhaust system 11 , in which an SCR catalyst system 20th is arranged for the reduction of nitrogen oxides. The SCR catalyst system 20th has an SCR catalytic converter 21 on. Exhaust gases leave the SCR catalytic converter 21 at its exit 22nd . In a reducing agent tank 23 is a reducing agent solution 24 stored in the form of a HWL. A suction line 25th opens into the reducing agent tank 23 . By means of a feed pump 26th becomes the reducing agent solution 24 through the suction line 25th sucked in and into a pressure line 27 promoted. From the pressure line 27 it is made using a metering valve 28 upstream of the SCR catalyst 21 in the exhaust system 11 dosed. A tank heater 30th in the form of a PTC thermistor (positive temperature coefficient) is at the bottom of the reducing agent tank 23 near the mouth of the suction line 25th arranged. There are also a reducing agent tank 23 a concentration sensor 31 and a level sensor 32 arranged. A temperature sensor 33 on the reducing agent tank 23 measures the temperature of the reducing agent solution 24 . An electronic control unit 40 controls the combustion engine 10 who have favourited the tank heater 30th and the feed pump 26th . It receives data from the concentration sensor 31 , the level sensor 32 and the temperature sensor 33 . It also receives data from a nitrogen oxide sensor 41 , the downstream of the exit 22nd of the SCR catalyst system 20th in the exhaust system 11 is arranged.

In one embodiment of the method according to the invention, which is shown in 2 is shown takes place after a start 40 of the internal combustion engine 10 an exam 41 whether the HWL 24 is frozen and therefore the tank heating 30th must be activated. The exam 41 can be done using a model. If the HWL 24 is frozen, another check is carried out 42 whether there are critical operating conditions. Critical operating conditions exist when it has been determined by means of an ambient temperature sensor (not shown) that the motor vehicle has been parked in a very cold environment at least for a predefinable period of time, the ambient temperature of which is below a first temperature threshold value. The critical operating conditions are also present when using the temperature sensor 33 it was found that a temperature in the reducing agent tank at least for a further predeterminable period of time 23 was below a second temperature threshold. Even if there is a signal from the concentration sensor 31 or the level sensor 32 in the electronic control unit 40 is not available, there are critical operating conditions. Based on a mass balance of by means of the metering valve 28 in the exhaust system 11 dosed reducing agent solution 24 is also in the electronic control unit 40 a model of the amount of liquid reducing agent solution 24 in the reducing agent tank 23 calculated. If this amount falls below a threshold value, then critical operating conditions are also present. As long as these critical operating conditions are not met, the internal combustion engine is operated 10 in a first operating state 43 . This corresponds to a conventional operating strategy for the internal combustion engine 10 . If, on the other hand, the critical operating conditions are present, the internal combustion engine will 10 in a second operating state 44 operated. In this the torque of the internal combustion engine is limited. This ensures that a statutory nitrogen oxide limit value at the output 22nd can be complied with without the risk that all of the reducing agent solution that has already thawed 24 is consumed. The existence of the critical operating conditions is constantly checked and, depending on whether these change, a change between the first operating state can be made several times 43 and the second operating state 44 respectively. This can in particular be caused by the driver's temporarily high torque demands on the internal combustion engine 10 be evoked. When the internal combustion engine 10 itself in its first operating state 43 is located and one more test 45 shows that the HWL 24 is now completely thawed, it is terminated 46 of the procedure.

In a second exemplary embodiment of the method according to the invention, it is in the second operating state 44 instead of limiting the torque provided that the internal combustion engine 10 is operated with a different map than in the first operating state 43 . This other map sees lower combustion temperatures and a higher EGR rate than the map of the first operating state 43 in front.

Claims (14)

Method for operating an internal combustion engine (10), wherein under predeterminable conditions during operation of a tank heater (25) of a reducing agent tank (23) of an SCR catalyst system (20) of the internal combustion engine (10) the internal combustion engine from a first operating state (43) to a second Operating state (44) is switched. Procedure according to Claim 1 , characterized in that the internal combustion engine (10) is operated in the second operating state (44) in such a way that raw nitrogen oxide emissions of the internal combustion engine (10) are reduced compared to the first operating state (43). Procedure according to Claim 1 or 2 , characterized in that a torque of the internal combustion engine (10) is limited in the second operating state (42). Method according to one of the Claims 1 to 3 , characterized in that the internal combustion engine (10) is operated in the second operating state (44) with a different map than in the first operating state (43). Method according to one of the Claims 1 to 4th , characterized in that a lower average combustion temperature of the internal combustion engine (10) and / or a higher EGR rate of the internal combustion engine are provided in the characteristic diagram of the second operating state (44) compared to the characteristic diagram of the first operating state (43). Method according to one of the Claims 1 to 5 , characterized in that the predeterminable conditions include that the phase state of a reducing agent solution in the reducing agent tank (23) was determined by a model as frozen or partially frozen. Method according to one of the Claims 1 to 6th , characterized in that the predeterminable conditions include that an ambient temperature of the reducing agent tank (23) falls below a predeterminable first temperature threshold value at least for a predeterminable first period. Method according to one of the Claims 1 to 7th , characterized in that the specifiable conditions include that a temperature of the reducing agent tank (23) falls below a specifiable temperature threshold value at least for a specifiable third period of time. Method according to one of the Claims 1 to 8th , characterized in that the predeterminable conditions include that a signal from a concentration sensor of the reducing agent tank is not available. Method according to one of the Claims 1 to 9 , characterized in that the predeterminable conditions include that a signal from a level sensor of the reducing agent tank is not available. Method according to one of the Claims 1 to 10 , characterized in that the predeterminable conditions include that a modeled amount of liquid reducing agent solution falls below an amount threshold value. Computer program which is set up, each step of the method according to one of the Claims 1 to 11 perform. Machine-readable storage medium on which a computer program is based Claim 12 is stored. Electronic control device (30) which is set up to use a method according to one of the Claims 1 to 11 to operate an internal combustion engine (10).

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